An apparatus which supports a wafer by gripping an outer edge of the wafer has hitherto been known as an apparatus which is to be attached to an extremity of an arm of a wafer transport robot and grips a wafer.
FIG. 3 shows a related-art example of such a wafer holding apparatus. In the drawing, reference numeral 1 designates a base material of the wafer holding apparatus. The base material 1 is a thin plate with a bifurcated extremity. Reference 2 designates an air cylinder which is secured on a root of the base material 1 and serves as drive means for actuating a pressing piece 3 attached to the extremity of the air cylinder in a longitudinal direction. The pressing element 3 is a member for pressing the outer edge of the wafer W, and the surface of the pressing element 3 to be brought into contact with the wafer W is flat. Reference numeral 4 designates an operation confirmation sensor which serves as detection means for checking operation of the air cylinder 2. Reference numeral 5 designates a wafer presence/absence sensor which checks presence or absence of a wafer W on the wafer holding apparatus. Reference numeral 6 designates stopper pins which are cylindrical stationary elements fixed at the respective extremities of the bifurcated portions of the base material 1. The stopper pins are for receiving a wafer W pressed by the pressing element 3. In other words, the wafer W is fixedly sandwiched between the pressing element 3 and the stopper pins 6. Reference numeral 7 designates support pins. Four support pins are fixed within a plane located between the pressing element 3 of the base material 1 and the stopper pins 6. The support pins 7 are cylindrical and have flat top faces and serve as support elements which support the weight of the wafer W while the wafer W is placed on the top faces.
Such a related-art wafer holding apparatus requires two types of sensors; that is, the operation confirmation sensor 4 and the wafer presence/absence sensor 5. Therefore, the accompanying complicated configuration of the wafer holding apparatus leads to a problem, such as a cost hike, an increase in weight, or deterioration in reliability.
A contact surface of the pressing element 3 is flat. Hence, there arises another problem in that, when the pressing element presses the wafer W, the wafer W sometimes leaps up while the stopper pins 6 serve as fulcrums, thereby causing difficulty in realization of stable holding.
The top faces of the support pins 7 are flat, leading to still another problem of a large contact area existing between the support pins 7 and the wafer W, thereby leading to adhesion of large amounts of particles.